Thomas a



(No Model.)

AVEDISON.

TELEPHONE. No. 329,030. Patented 001:. 27, 1885.

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UNITED STATES PATENT OFFICE.

THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY.

TELEPHONE.

SPECIFICATION forming part of Letters Patent No. 329,030, dated October27, 1885 Application filed December 15, 1884. Serial No. 150,344. (Nomodel.)

To all whom it may concern:

Be it known that I, THOMAS A. Enrson, of Menlo Park, in the county ofMiddlesex and State of New Jersey, have invented a new and usefulImprovement in Telephones, (Case No. 636,) of which the following is aspecification.

In the use of loose granulated carbon or other divided conductingmaterial in telephones such material is liable to shift its position andbecome packed, and theinstrument be thereby made to fail in itsoperation. This renders it necessary to fix the position of suchinstruments, which is not desirable, and eyen when their position isfixed the difficulty is not wholly overcome, since external vibrationsserve to produce thesame result. I have found, however, that by coatingto the minimum extent the carbon or other granules with an adhesivesubstancesuch as an oil or other viscous material-the effectiveness ofthe instrument is not injured, and the granules will retain theirrelative positions without packing. This discovery is applicable to anyform of telephone in which granulated carbon or other material is used,and hence Iwish it understood that my invention is not limited to anyparticular construction of instrument.

In the accompanying drawing, to which reference is now made, there isshown, for illus- .tration, a sectional view of a conventional form oftelephone.

Ais a metal diaphragm, between which and a metal back plate, B, islocated a body, 0, of loose granules of carbon or other conductingmaterial. These granules are coated with an adhesive substance, asalready explained. The circuit-connections l 2 are made with the diaphragm and back plate, the body of granulated carbon or other materialbeing interpolated in the circuit between those parts.

What I claim is 1. A telephone having in circuit a body of granulatedmaterial, the granules being coated with an adhesive substance,substantially as set forth.

2. A telephone having in circuit a body of granulated carbon, the carbongranules being coated with an adhesive substance, substantially as setforth.

This specification signed and witnessed this 3d day of December, 1884.

THOMAS A. EDISON.

Witnesses:

THOS. G. GREENE, J r., EDW. O. ROWLAND.

